Tool identification

ABSTRACT

A tool joint part has a PIC incorporated therein for storing data which can be used to identify the tool to which the joint part is interconnected. PICs are incorporated into tool conditioning circuits. An intermediate circuit operates to match the identity stored digitally in a first PIC with the identity stored digitally in another PIC and thereby connect the tool to the appropriate tool conditioning circuit.

BACKGROUND

This invention relates to the identification of tools, e.g. measurementtools used for inspection of work pieces on a co-ordinate positioningmachine. Such co-ordinate positioning machines include co-ordinatemeasurement machines (CMM's), machine tools and robots.

Measurement tools, e.g. probes that respond to surface contact, surfacefinish probes, proximity probes, crack detection probes, laser and otheroptical measuring probes, video cameras etc, all have individualrequirements for the conditioning of their respective signals. Where amachine uses more than one tool, e.g. each tool being connectable to auniversal mounting then it is desirable to have a means foridentification of the tool that is mounted to the machine so that itssignal can be conditioned correctly. Contact probes sometimes useextension bars and these too require identification.

SUMMARY

One approach to tool identification is described in EP236414. In thatpatent there is disclosed a tool identification system including a toolhaving contacts connected to an electrical resistance of a valuecorresponding to that particular tool type. When the tool is mounted tothe machine the connections on the tool make with complementaryconnections on a universal mounting and the tool is interrogated. Theresistance of the tool is measured and the type of tool can thus berecognised by the machine. The appropriate interface circuit for thattype of tool can then be selected.

With increasing numbers of types of tool the limitations of this systemhave become apparent. Use of a standard resistor value series results ina limit to the number of resistance values that can be used and therebya limit to the number of types of tool that can use such anidentification system. Furthermore, errors in resistance values, e.g.due to poor manufacturing tolerance, age of the resistor, or unwantedresistance at the tool connections, can all lead to an incorrectrecognition of the type of tool mounted to the machine.

According to one aspect of the invention there is provided a toolidentification apparatus comprising:

a first part of a tool joint including a first electrical connection anda releasable mounting, said first part being for releasable coupling toa tool head having a second part of the joint which has a complementarymounting and a second electrical connection;a tool identification data storage device for storing digitally toolidentification data; anda data communication link between the said electrical connection and thesaid tool identification data storage device for carrying saididentification data.

Preferably the data storage device is non-volatile memory.

Preferably the tool identification data storage device comprises a PICdevice and wherein the data communication link comprises two conductivepaths only.

Preferably the identification data storage device is located at thereleasable joint.

Preferably the first part further includes a connector forinterconnecting the part to a tool.

Preferably the two conductive paths provide a path for tool power aswell as the data communication link.

According to another aspect the invention provides a tool identificationsystem comprising:

tool identification apparatus according to the said one aspect andfurther comprising:

a tool holding head, the head having a second part of the tool jointhaving a further mounting for releasably coupling to the first part tothe second part, the second part of the joint including a secondelectrical connection complementary to the first electrical connectionfor carrying the identification data.

Preferably the tool identification system further comprises:

at least one interface circuit having interface circuit identificationdata storage for storing interface circuit identification data, the oreach interface circuit in use conditioning signals provided by a tool;and

an intermediate circuit in further data communication with both thesecond electrical connection and the or each interface circuit, in usethe intermediate circuit being operable to provide an electrical linkbetween the tool and the said at least one interface circuit if the saidtool identification data corresponds with the said interface circuitidentification data.

Preferably the intermediate circuit is further operable to provide afurther link between the tool and a further interface circuit if noidentification data is obtained.

According to yet another aspect the invention provides a toolidentification system comprising:

a tool holding head, having a second part of a releasable joint; and

at least one tool, each tool having a tool identification moduleconnected to the or each tool, the or each tool identification modulehaving a first part of a releasable joint for coupling to the secondpart of the joint on the head, a connector for interconnecting the toolto the module, and a digital data store for identifying the tool towhich the module is connected.

The invention extends to a module for interconnecting both electricallyand mechanically a tool to a tool head, wherein the module has a digitaldata store for identifying the tool to which it is connected.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will now be described with reference tothe drawings, wherein:

FIG. 1 shows a CMM with interchangeable measuring probes, incorporatingthe invention, and;

FIG. 2 shows a schematic illustration of the electrical arrangement ofthe invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a known CMM 5 having a head 10 with a releasable kinematicjoint 17/18. The lower part 18 of the joint will be common to a numberof measurement tools 12, in this case measurement probes 12 a, 12 b and12 c, and has a kinematic mounting attachable to the upper part of thejoint 17. Both parts 17 and 18 will have complementary kinematicmounting features.

Kinematic features are shown in a publication by H. J. J. Braddickcalled “Mechanical Design of Laboratory Apparatus”, Chapman & HallLimited, 1960 and may additionally include quasi or semi-kinematicdesigns. As an example of a kinematic mounting there is shown on each ofthe lower parts 18 three equispaced balls 26, each of which sit in acomplementary vee slot 27 on the upper mounting of the joint part 17.The balls and slots are arranged in a triangular formation so six pointsof contact are made between the mountings at the upper and lower jointparts 17/18. Other kinematic and semi/quasi-kinematic configurations arepossible within the ambit of the invention, e.g. three balls contactinga triangular hole, a vee slot and a flat plate respectively.

The CMM has a head 10 which can be moved under the instruction ofcontroller 51 in any of the X, Y or Z directions illustrated and therebyinspect the dimensions of a workpiece 7, sat on base 11, by means ofcontact of the workpiece by stylus 14 attached to probe 12 a. The CMM isalso capable of exchanging automatically the probe 12 a for anotherprobe 12 b,12 c housed in a rack 40. The kinematic joint providesrepeatable repositioning of probes removed and replaced onto the head10.

One mechanism for automatic exchange and locking/unlocking of the probeto and from kinematic mounting of joint part 17 is described in detailin WO85/02138. The disclosure in that patent document is incorporatedherein. Other joints and mountings can be used. Manual exchange ofprobes may also be employed. When a rack is used an operator is requiredinitially to place the probes 12 into the rack 40 and this may be donein the incorrect order. Manual exchange of probes may also lead to thewrong probe being fitted to the machine.

Referring also to FIG. 2 an intermediate circuit, in this case amicroprocessor 20, is used in this invention to interrogate probe 12mounted to the head 10 via communication line 9 in order that it can berecognised. Additionally the microprocessor 20 also interrogates probeinterface circuits 23A,B and C via communication lines 33 to recogniseeach circuit 23 in order that the signals from the probe along line 30can be routed to the correct interface circuit by relay switches atcircuit 22. From the appropriate interface circuit the signal is fed tothe CMM controller 51 via lines 25 and optionally to a computer forprocessing of data.

The identification of the probes 12 and interface circuits 23 ispossible because a data store 19 and 32 is held in each probe andinterface circuit respectively. The data store is digital information incode form held in a non-volatile memory which can identify theprobe/interface. This data store is read by the microprocessor 20, andthe microprocessor operates ranks of switches (relays) 22 so thatinformation to and/or from the probe is communicated to/from the correctinterface.

Since it is likely that the data store will be incorporated intodifferent types of tools, it is convenient to locate the data store inthe releasable joint part 18 so that the joint part can be standardisedand used in all types of tool and no modifications to other parts of thetool will be required. Thus the joint part 18 may have a modular form,i.e. a discrete component which can be sold separately. This toolidentification module will have a digital data store (e.g. aprogrammable integrated circuit (PIC)) which is programmed or isprogrammable so that it can identify the tool to which it is attached.

Each joint part 18 will have, as well as its kinematic features, a toolconnector 21 for interconnecting the various tools e.g. 12 a,b and c tothe joint part 18. The connector could be a simple screw type fixing.

FIG. 2 shows in more detail the electrical arrangement illustrated inFIG. 1. In this Fig the tools 12 a,b and c can be seen housed in rack40. The tools (including probe 12 a) have electrical contacts 16 at thereleasable joint part 18 that co-operate with complimentary contacts 15on the universal mounting of the joint part 17. Two of the contacts 16are connected to probe data store 19, in this instance a programmableintegrated circuit (PIC). The PIC has a digital code embedded in memorytherein which can be recognised by the processor 20. A similar PIC 32 isused as a data store in each interface circuit 23 and likewise, theprocessor 20 can recognise a code embedded in the PIC 32.

An advantage of using a PIC is that just two wires 28 or otherconductive paths can be employed to carry the stored data andinterrogate the PIC, via a serial interface and these wires, at the toolat least, can be used for probe power also. Additionally the use of twowires means that backward compatibility is possible i.e. the probe etc,previously fitted with a resistor identification (as detailed in thediscussion of the prior art) can be recognised also by the processor 20.In such circumstances the processor 20 can be adapted to measure theresistance of the two wires. If the resistance varies from a known valueused to denote a digital identification (i.e. the tool is an “old”resistance identified probe) then the processor can route a toolcommunication to a pre-defined port of the intermediate circuit 20. Thisport may be in communication with an appropriate interface 23, or may bein communication with a further intermediate circuit for selecting oneof a number of interfaces depending on the resistance of the tool in thehead 10. Thus a digital system of tool identification can be madebackwardly compatible with the known resistance type identificationsystem.

Additionally, it may be desirable to make a group of tools compatiblewith a single (or a few) interface circuit(s), or vice versa. This canbe achieved by adding identification codes, but not necessarily anadditional PIC to the interface so that effectively it has more than oneidentity, each of which will be pairable with a code from a member ofthe compatible group of tools, or vice versa.

1. A measurement tool identification system comprising: a co-ordinatepositioning machine including a intermediate circuit, a measurement toolholding head, the head including a first joint part having a firstreleasable mounting and a first electrical connection in electricalcommunication with the intermediate circuit, and at least one interfacecircuit in electrical communication with the intermediate circuit, forconditioning the outputs of a tool, the at least one interface circuithaving an interface circuit identification device; a second joint partincluding a second releasable mounting and a second electricalconnection, each being complementary with the mounting and connection ofthe first joint part, the second joint part including a measurement toolidentification device, the tool and circuit identification devices eachcomprising a digital data store and wherein the intermediate circuitinterrogates the digital data stores of the tool and interface circuitidentification devices in order to identify the tool and interfacecircuits and electrically connects the appropriate interface circuit tothe second joint part following the identification.
 2. The measurementtool identification system of claim 1, comprising the data storagedevice being non-volatile memory.
 3. The measurement tool identificationsystem of claim 2, comprising the digital data stores each including aprogrammable device and electrical communication between theintermediate circuit and the second joint part comprises only twoconductive paths.
 4. The measurement tool identification system of claim2, comprising the measurement tool identification device being locatedwithin the second joint part.
 5. The measurement tool identificationsystem of claim 1, comprising the digital data stores each including aprogrammable device and electrical communication between theintermediate circuit and the second joint part comprises only twoconductive paths.
 6. The measurement tool identification system of claim5, comprising the two conductive paths providing a path for measurementtool power as well as data for tool identification.
 7. The measurementtool identification system of claim 5, comprising the measurement toolidentification device being located within the second joint part.
 8. Themeasurement tool identification system of claim 1, comprising themeasurement tool identification device being located within the secondjoint part.
 9. The measurement tool identification system of claim 8,comprising the second joint part including a connector forinterconnecting the second joint part to a measurement tool.
 10. Themeasurement tool identification system of claim 9, comprising thecomplementary releasable mountings of the first and second joint partsforming a kinematic mounting.
 11. The measurement tool identificationsystem of claim 10, comprising the intermediate circuit being operableto electrically connect the tool and another interface circuit if noidentification data is obtained during interrogation.
 12. Themeasurement tool identification system of claim 10, comprising theintermediate circuit being operable to electrically connect the tool andanother interface circuit if the resistance across the second electricalconnection varies from a predefined value used to denote digitalidentification.
 13. A measurement tool including a joint part comprisinga portion of a releasable kinematic mounting and a portion of anelectrical connection, each portion being co-operable with acomplementary portion on a co-ordinate positioning machine, the toolfurther including a first digital data store for holding a digital toolidentification code, in combination with an interface circuit for thetool which comprises a second digital data store for holding a digitalinterface circuit identification code, whereby when the tool isconnected to the co-ordinate positioning machine and interrogatedthereby, the tool digital identification code identifies the tool andindicates that the tool is to be electrically connected to saidinterface circuit having said digital interface circuit identificationcode.
 14. The measurement tool of claim 13, wherein the tool has apredefined resistance that, when connected to the coordinate positioningmachine and interrogated thereby, indicates that the tool contains saiddigital tool identification code.